1. Field of the Invention
This invention relates to electrical connector assemblies for cables having a plurality of insulated conductors, and to socket connector assemblies for electrical connection to such connector assemblies, and is more particularly, but not exclusively, concerned with such connector and socket assemblies for use with electric submersible pumps and compressors.
2. Description of the Related Art
Electric submersible pumps (ESP) are installed in subterranean wells for extracting hydrocarbons where the natural pressure in the reservoir is insufficient to lift the fluid or gas to the surface. The ESP motor is powered through a cable that connects the motor to a power source at the surface. The cable is connected to the motor by means of a detachable electrical connector assembly designed to provide electrical integrity and to seal the motor against the ingress of well fluids.
U.S. Pat. No. 5,567,170 discloses a plug-in type electrical connector assembly that can be used to connect the cable to the ESP motor. In this arrangement the motor is provided with a machined port, called a pothole, and the motor windings are terminated at a socket assembly within the pothole into which the connector assembly can be plugged. In this case the pothole is a single round hole containing a single socket connector block containing terminals that are connected to the motor windings by means of braided wire leads. The socket connector block is mechanically secured to the motor housing independently of its connection to the windings.
The connector assembly terminating the power cable that is run from the surface, called the pothead, is inserted into the pothole and is sealed against the ingress of well fluids by an elastomeric gasket or an O-ring.
The pothole is machined at an angle to the axis of rotation of the motor for ease of manufacturing. However, the angled pothole limits the length of the mating electrical parts of the connector and socket assemblies, and consequently limits the length of insulating material that can be provided around the parts to provide a long creepage distance between the outside of the connector assembly and the electrical interface between the connector and socket assemblies. It is important to provide as long a creepage distance as practically possible as a significant failure mechanism in such connection arrangements is electrical tracking from the live electrical parts to the motor housing, exacerbated by ingress of moisture after operation over many months or years.
Furthermore, because the primary seal with respect to each conductor from the cable bears against the conductor insulation and the conductor insulation is liable to swell when subjected to the high temperature environment of the well, the seal integrity is compromised.
U.S. Pat. No. 6,676,447 discloses a further plug-in type electrical connector assembly for an ESP motor in which three insulated conductors from the cable extend through three separate passages in a first insulating block and are sealed within these passages by means of separate washers compressed by three protrusions extending from a second insulating block screwed to the first insulating block. Such an arrangement suffers from the fact that the primary seal with respect to each conductor bears against the conductor insulation and the conductor insulation is liable to swell when subjected to the high temperature environment of the well. Furthermore, as the elastomeric materials of the insulation and the seal increase in volume, the insulation can be damaged or the seal integrity diminished.
U.S. Pat. No. 3,997,232 discloses a motor connector assembly that is attachable to the top of the motor housing by way of a pothole extending parallel to the motor axis. Motors with thrust bearings in the top cannot have the connector on top of the motor as it is not possible for the three insulated conductors from the cable to be passed beyond the bearing. However the three insulated conductors from the cable extend through three parallel passages in a common sealing gland, and thus there are again difficulties in terms of the integrity of the seals in a downhole environment.
U.S. Pat. No. 4,204,739 discloses a motor connector assembly having separate potholes for each conductor. Each conductor is provided with a strain relief and seal assembly that is tightened in the motor head independently of the assemblies of the other conductors. However each of the conductors is sealed within the corresponding pothole by a respective O-ring seal, so that there are difficulties in assembly as well as in the integrity of the sealing as a result of the direct sealing of the O-ring seal on the conductor insulation. Also there is insufficient strain relief for the conductors with the result that there is a risk that the conductors will be pulled out of the motor when it is installed in a well.
U.S. Pat. No. 5,700,161 discloses a two-piece pothead casting that is assembled in two halves and that is split radially across the conductors. However the three insulated conductors from the cable extend through three passages in a common insulating block, and thus there are again difficulties in terms of the integrity of the sealing in a downhole environment. Typically, in such arrangements, the motor head, within which the pothole is formed, is required to be screwed into the tubular motor housing during assembly. This means that there is little control over the relative rotational positions of the pothole and the motor stator within the housing. Furthermore the flexible leads connecting the stator windings to the socket connector block within the pothole tend to be wound around the motor shaft as the motor head is screwed into the motor housing, a protective tube being provided to separate the leads from the shaft. Such winding of the leads around the motor shaft during assembly can introduce further possible failure mechanisms, and it is not possible to observe the twisted motor leads and their connection to the stator windings once the motor head has been assembled with the motor housing. Any resulting chafing, cuts or strain on the internal electrical joints may not be revealed during initial electrical testing but may remain as a weak point during long-term service.
It is an object of the invention to provide an electrical connector assembly and corresponding electrical socket assembly that avoids many of the pitfalls associated with known assemblies.